The wisdom behind drinking whilst sitting

It is permissible to drink both sitting and standing,
although drinking whilst sitting is better, and it is what the Prophet
(blessings and peace of Allah be upon him) did most often. This has been
discussed in the answer to question number
21147. 

Ibn al-Qayyim (may Allah have mercy on him) said, explaining
the negative effect of drinking whilst standing and the importance of
drinking whilst sitting: 

Drinking whilst standing has numerous negative effects, one
of which is that it does not fully quench the thirst and does not settle in
the stomach so that the liver can distribute the nutrients to other parts of
the body. Rather it comes to the stomach with speed and force, and there is
the fear that it will cause a chill or disturbance, and may pass quickly to
the lower parts of the body without moving gradually. All of that is harmful
to the drinker, but if he does it occasionally or in the case of need, it
will not harm him… End quote from Zaad al-Ma‘aad, 4/229. 

Al-Tahhaawi (may Allah have mercy on him) said:

It was narrated that al-Sha‘bi said: Drinking whilst standing
is only disliked because it is harmful. And al-Sha‘bi gave the reason for
which this is not allowed: because of the fear of either harm and disease
that results from that, and nothing else. In forbidding that, the Messenger
of Allah (blessings and peace of Allah be upon him) was motivated by
compassion for his ummah and sought to tell them to do that which is in
their best interests in both religious and worldly terms, as he said to
them, “As for me, I do not eat reclining.” That does not mean that it is
haraam for them to do that, rather the meaning is that there is some fear
for them if they eat reclining. Al-Sha‘bi mentioned the reason why the
Messenger of Allah (blessings and peace of Allah be upon him) disliked
eating reclining, and it is only because of what happens as a result, such
as enlargement of the belly. The same is true of what was narrated from him
about the prohibition on drinking whilst standing; it is only because of
what may result from that and he disliked it for that reason and no other.
End quote from Sharh Ma‘aani al-Aathaar, 4/274 

What the believer should do is follow the guidance and Sunnah
of the Prophet (blessings and peace of Allah be upon him), whether he knows
the wisdom behind it or not; there is nothing wrong with asking about the
reason or looking for it so as to increase his faith or to debate, in the
way that is better, with those who reject this Sunnah. 

And Allah knows best.